So we are comfortable with the numbers on the front of our lens, we understand what aperture is and how we can use it creatively, we are able to use (and manipulate) our autofocus to ensure that we are focusing in the right region, and finally we understand how important shutter speed is in obtaining a sharp image (or creating something a bit more abstract perhaps).
With shutter speed, we understand that too slow a shutter speed (as is often the case in low light) can result in soft and blurry images. We know that we need a faster shutter speed in order to cancel out any camera movement but also understand that we may not want to, or be able to, change our aperture value to allow in any more light (in order to increase the shutter speed).
This brings us to ISO.
I like to look at ISO as the “middle-man” which brokers a deal between aperture and shutter speed.
You’ve set your desired aperture based on your resultant depth of field.
The camera has metered the scene and decided on a suitable shutter speed which will ensure that the entire scene is correctly exposed.
Unfortunately, the light is such that the camera needs to use a slower shutter speed to allow enough light in and this has the potential to create camera shake. We don’t want that.
Enter ISO, or the middleman, to broker a deal.
ISO is a variable which takes place in the camera and results in the sensor becoming more sensitive to the available light. In essence the higher the ISO value, the more sensitive the sensor is to light.
So, if the camera gave you a shutter speed of 1/30th of a second at an ISO value of 100, you would be able to achieve a much faster shutter speed by increasing the ISO value to something like ISO 2000.
The take home message here is that ISO can be used as a trump card/broker to achieve the desired shutter speed without changing your aperture value.
Why Not Shoot at High ISO Values all the Time then?
Good question as shooting at ISO values of 2000 or more would result in much faster shutter speeds.
There is a down side to high ISO values though. Noise.
Digital noise to be precise. This “noise” presents itself in two ways, colour noise (the red green and blue flecks which you can see below) and luminance noise (the grain that you can see below).
This noise is a by product of the technical processes that needs to take place in order for the sensor to become more sensitive to light. Its not ideal but its also not the end of the world.
Post processing software such as Lightroom is incredibly good at dealing with noise and by adjusting two sliders in the detail panel we can deal with both colour and luminance noise to “save” any images with high levels of noise.
So what’s the take home message on ISO?
Go as high as necessary but stay as low as possible.
That is to say that if this was your first time to ever see Wld Dog in the wild, push your ISO to 10 000 if you have to in order to get a sharp shot.
Yes the image will have noise but you can still work with that. As technology progresses, cameras are becoming better and better at dealing with noise at high ISO values. If it means the difference between getting the shot and missing it, go as high as you have to!
If you don’t want to fight the light with ISO then you can get creative and intentionally capture movement with the resultant shutter speed.
So, thats ISO in a nutshell.
Here are a couple of other interesting articles on ISO which you may find useful.
- Do you fight the light or work with it?
- ISO, are we still making noise about this in 2016?
- Do not fear ISO!
- ISO 800 to 4000 in 15 minutes
Remember, this is a back to basics series and there is a lot more to ISO than what I have presented here but, if you can grasp this then you’re already well on your way to moving your photography!
A Recap on your process before capturing an image in Aperture Priority:
- Evaluate the scene and decide what Aperture value you will use (small number = shallow depth of field)
- Move your focus point to the desired region and half depress, ensuring that your subjects is in focus
- With your focal length in mind, check the shutter speed given by the camera
- If your shutter speed is less than 1/focal length, increase your ISO
- If your shutter speed seems way faster than what you need, reduce your ISO
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